Like his Canadian compatriot Cronenberg, Atom Egoyan has often made films about sex that are (deliberately) unsexy, approaching the subject with a clinical detachment (Exotica, for instance, is a very good film, but if you're looking for a sexy film about strip clubs, you've probably got the wrong film). With Chloe, which is easily his highest profile project in terms of acting talent (Julianne Moore, Liam Neeson, Ms. Seyfried), Egoyan seems to be trying to maintain some semblance of a grip on his usual tones and themes while still delivering a (more or less) mainstream product which is, at its core, essentially an erotic thriller about obsession with a plot not-so-different from any dozen other films of that type (and a remake of a French film which I have not seen). Anyway, Egoyan's attempt to fuse his usual "arthouse" sensibilty with the mainstream is not very successful.
The plot in a sentence: Julianne Moore believes her husband (Neeson) has been cheating on her so she hires a lovely young escort/prostitute (Seyfried as the titular Chloe) to pose as a flirt and test his inclinations. The film is at its best in the sections where Seyfried verbally relates (often graphically) her discoveries to Moore. Here we see Egoyan's interests in the manipulation of point-of-view emerging, but unlike his earlier, better films, this time it's mainly used in the service of the film's obligatory thriller "twist," such as it is (you'll see it coming far in advance). By the time Chloe arrives at its laughable final moments, no one is likely to feel much investment in it (the motivations of the characters alternate between unbelievable--Moore--and deliberately inscrutable--Chloe). But let's end by addressing the reason that a few people will be drawn to the theater for this: yes, you see Seyfried naked early and often and complete with a lesbian scene.